This application claims priority, under 35 U.S.C. 119, of earlier-filed Japanese Application No. 63973/1992, filed Mar. 19, 1992.
The present invention relates to hydraulic power steering systems, and more particularly, to such a system including a steering control valve having an input detection device.
Conventional hydraulic power steering systems are already well known to those skilled in the art, and are illustrated and described in U.S. Pat. Nos. 4,034,419 and 5,020,618, both of which are assigned to the assignee of the present invention and incorporated herein by reference.
The typical hydraulic power steering system includes a steering control unit having directional control valving, comprising a spool and a sleeve, operated by an input such as a steering wheel. A steering cylinder is connected to the steering control unit through right and left hydraulic lines. A source supplies pressurized fluid for the steering cylinder through a hydraulic line connected to the steering control unit. The steering unit includes a housing having inlet and outlet ports and right and left control fluid ports, and a fluid meter having internally and externally-toothed members. The directional control valving controls fluid communication between the various ports and the fluid meter.
In the application of many such hydraulic power steering systems, it is especially desirable to be able to detect the torque being applied to the input to the steering unit, i.e., the torque being applied to the input shaft which connects the steering wheel to the spool of the directional valving. Typically, it is necessary that the detection of the input torque be fairly accurate.
In order to meet such requirements, those skilled in the art have developed various system modifications requiring parts to be added to the steering control unit. This results in additional complication and cost of the overall system. Those skilled in the art have also attempted to perform torque or input detection by sensing the pressure at the inlet port of the steering control valve. However, this is typically not accurate enough because of variations in the pump discharge pressure and the amount of opening of the control orifices in the steering valve.